#define N_IN_URB       4
 #define N_OUT_URB      4
 #define IN_BUFLEN      4096
-#define OUT_BUFLEN     128
 
 struct sierra_port_private {
+       spinlock_t lock;        /* lock the structure */
+       int outstanding_urbs;   /* number of out urbs in flight */
+
        /* Input endpoints and buffer for this port */
        struct urb *in_urbs[N_IN_URB];
        char in_buffer[N_IN_URB][IN_BUFLEN];
-       /* Output endpoints and buffer for this port */
-       struct urb *out_urbs[N_OUT_URB];
-       char out_buffer[N_OUT_URB][OUT_BUFLEN];
 
        /* Settings for the port */
        int rts_state;  /* Handshaking pins (outputs) */
        int dsr_state;
        int dcd_state;
        int ri_state;
-
-       unsigned long tx_start_time[N_OUT_URB];
 };
 
 static int sierra_send_setup(struct usb_serial_port *port)
        return -ENOIOCTLCMD;
 }
 
+static void sierra_outdat_callback(struct urb *urb)
+{
+       struct usb_serial_port *port = urb->context;
+       struct sierra_port_private *portdata = usb_get_serial_port_data(port);
+       int status = urb->status;
+       unsigned long flags;
+
+       dbg("%s - port %d", __FUNCTION__, port->number);
+
+       /* free up the transfer buffer, as usb_free_urb() does not do this */
+       kfree(urb->transfer_buffer);
+
+       if (status)
+               dbg("%s - nonzero write bulk status received: %d",
+                   __FUNCTION__, status);
+
+       spin_lock_irqsave(&portdata->lock, flags);
+       --portdata->outstanding_urbs;
+       spin_unlock_irqrestore(&portdata->lock, flags);
+
+       usb_serial_port_softint(port);
+}
+
 /* Write */
 static int sierra_write(struct usb_serial_port *port,
                        const unsigned char *buf, int count)
 {
-       struct sierra_port_private *portdata;
-       int i;
-       int left, todo;
-       struct urb *this_urb = NULL; /* spurious */
-       int err;
+       struct sierra_port_private *portdata = usb_get_serial_port_data(port);
+       struct usb_serial *serial = port->serial;
+       unsigned long flags;
+       unsigned char *buffer;
+       struct urb *urb;
+       int status;
 
        portdata = usb_get_serial_port_data(port);
 
        dbg("%s: write (%d chars)", __FUNCTION__, count);
 
-       i = 0;
-       left = count;
-       for (i=0; left > 0 && i < N_OUT_URB; i++) {
-               todo = left;
-               if (todo > OUT_BUFLEN)
-                       todo = OUT_BUFLEN;
-
-               this_urb = portdata->out_urbs[i];
-               if (this_urb->status == -EINPROGRESS) {
-                       if (time_before(jiffies,
-                                       portdata->tx_start_time[i] + 10 * HZ))
-                               continue;
-                       usb_unlink_urb(this_urb);
-                       continue;
-               }
-               if (this_urb->status != 0)
-                       dbg("usb_write %p failed (err=%d)",
-                               this_urb, this_urb->status);
+       spin_lock_irqsave(&portdata->lock, flags);
+       if (portdata->outstanding_urbs > N_OUT_URB) {
+               spin_unlock_irqrestore(&portdata->lock, flags);
+               dbg("%s - write limit hit\n", __FUNCTION__);
+               return 0;
+       }
+       portdata->outstanding_urbs++;
+       spin_unlock_irqrestore(&portdata->lock, flags);
+
+       buffer = kmalloc(count, GFP_ATOMIC);
+       if (!buffer) {
+               dev_err(&port->dev, "out of memory\n");
+               count = -ENOMEM;
+               goto error_no_buffer;
+       }
 
-               dbg("%s: endpoint %d buf %d", __FUNCTION__,
-                       usb_pipeendpoint(this_urb->pipe), i);
+       urb = usb_alloc_urb(0, GFP_ATOMIC);
+       if (!urb) {
+               dev_err(&port->dev, "no more free urbs\n");
+               count = -ENOMEM;
+               goto error_no_urb;
+       }
 
-               /* send the data */
-               memcpy (this_urb->transfer_buffer, buf, todo);
-               this_urb->transfer_buffer_length = todo;
+       memcpy(buffer, buf, count);
 
-               this_urb->dev = port->serial->dev;
-               err = usb_submit_urb(this_urb, GFP_ATOMIC);
-               if (err) {
-                       dbg("usb_submit_urb %p (write bulk) failed "
-                               "(%d, has %d)", this_urb,
-                               err, this_urb->status);
-                       continue;
-               }
-               portdata->tx_start_time[i] = jiffies;
-               buf += todo;
-               left -= todo;
+       usb_serial_debug_data(debug, &port->dev, __FUNCTION__, count, buffer);
+
+       usb_fill_bulk_urb(urb, serial->dev,
+                         usb_sndbulkpipe(serial->dev,
+                                         port->bulk_out_endpointAddress),
+                         buffer, count, sierra_outdat_callback, port);
+
+       /* send it down the pipe */
+       status = usb_submit_urb(urb, GFP_ATOMIC);
+       if (status) {
+               dev_err(&port->dev, "%s - usb_submit_urb(write bulk) failed "
+                       "with status = %d\n", __FUNCTION__, status);
+               count = status;
+               goto error;
        }
 
-       count -= left;
-       dbg("%s: wrote (did %d)", __FUNCTION__, count);
+       /* we are done with this urb, so let the host driver
+        * really free it when it is finished with it */
+       usb_free_urb(urb);
+
+       return count;
+error:
+       usb_free_urb(urb);
+error_no_urb:
+       kfree(buffer);
+error_no_buffer:
+       spin_lock_irqsave(&portdata->lock, flags);
+       --portdata->outstanding_urbs;
+       spin_unlock_irqrestore(&portdata->lock, flags);
        return count;
 }
 
                if (port->open_count && status != -ESHUTDOWN) {
                        err = usb_submit_urb(urb, GFP_ATOMIC);
                        if (err)
-                               printk(KERN_ERR "%s: resubmit read urb failed. "
-                                       "(%d)", __FUNCTION__, err);
+                               dev_err(&port->dev, "resubmit read urb failed."
+                                       "(%d)", err);
                }
        }
        return;
 }
 
-static void sierra_outdat_callback(struct urb *urb)
-{
-       struct usb_serial_port *port;
-
-       dbg("%s", __FUNCTION__);
-
-       port = (struct usb_serial_port *) urb->context;
-
-       usb_serial_port_softint(port);
-}
-
 static void sierra_instat_callback(struct urb *urb)
 {
        int err;
 
 static int sierra_write_room(struct usb_serial_port *port)
 {
-       struct sierra_port_private *portdata;
-       int i;
-       int data_len = 0;
-       struct urb *this_urb;
+       struct sierra_port_private *portdata = usb_get_serial_port_data(port);
+       unsigned long flags;
 
-       portdata = usb_get_serial_port_data(port);
+       dbg("%s - port %d", __FUNCTION__, port->number);
 
-       for (i=0; i < N_OUT_URB; i++) {
-               this_urb = portdata->out_urbs[i];
-               if (this_urb && this_urb->status != -EINPROGRESS)
-                       data_len += OUT_BUFLEN;
+       /* try to give a good number back based on if we have any free urbs at
+        * this point in time */
+       spin_lock_irqsave(&portdata->lock, flags);
+       if (portdata->outstanding_urbs > N_OUT_URB * 2 / 3) {
+               spin_unlock_irqrestore(&portdata->lock, flags);
+               dbg("%s - write limit hit\n", __FUNCTION__);
+               return 0;
        }
+       spin_unlock_irqrestore(&portdata->lock, flags);
 
-       dbg("%s: %d", __FUNCTION__, data_len);
-       return data_len;
+       return 2048;
 }
 
 static int sierra_chars_in_buffer(struct usb_serial_port *port)
 {
-       struct sierra_port_private *portdata;
-       int i;
-       int data_len = 0;
-       struct urb *this_urb;
-
-       portdata = usb_get_serial_port_data(port);
-
-       for (i=0; i < N_OUT_URB; i++) {
-               this_urb = portdata->out_urbs[i];
-               if (this_urb && this_urb->status == -EINPROGRESS)
-                       data_len += this_urb->transfer_buffer_length;
-       }
-       dbg("%s: %d", __FUNCTION__, data_len);
-       return data_len;
+       dbg("%s - port %d", __FUNCTION__, port->number);
+
+       /*
+        * We can't really account for how much data we
+        * have sent out, but hasn't made it through to the
+        * device as we can't see the backend here, so just
+        * tell the tty layer that everything is flushed.
+        */
+       return 0;
 }
 
 static int sierra_open(struct usb_serial_port *port, struct file *filp)
                }
        }
 
-       /* Reset low level data toggle on out endpoints */
-       for (i = 0; i < N_OUT_URB; i++) {
-               urb = portdata->out_urbs[i];
-               if (! urb)
-                       continue;
-               urb->dev = serial->dev;
-               /* usb_settoggle(urb->dev, usb_pipeendpoint(urb->pipe),
-                               usb_pipeout(urb->pipe), 0); */
-       }
-
        port->tty->low_latency = 1;
 
        /* set mode to D0 */
                /* Stop reading/writing urbs */
                for (i = 0; i < N_IN_URB; i++)
                        usb_unlink_urb(portdata->in_urbs[i]);
-               for (i = 0; i < N_OUT_URB; i++)
-                       usb_unlink_urb(portdata->out_urbs[i]);
        }
        port->tty = NULL;
 }
                        port->bulk_in_endpointAddress, USB_DIR_IN, port,
                        portdata->in_buffer[j], IN_BUFLEN, sierra_indat_callback);
                }
-
-               /* outdat endpoints */
-               for (j = 0; j < N_OUT_URB; ++j) {
-                       portdata->out_urbs[j] = sierra_setup_urb (serial,
-                       port->bulk_out_endpointAddress, USB_DIR_OUT, port,
-                       portdata->out_buffer[j], OUT_BUFLEN, sierra_outdat_callback);
-               }
        }
 }
 
                if (!portdata) {
                        dbg("%s: kmalloc for sierra_port_private (%d) failed!.",
                                        __FUNCTION__, i);
-                       return (1);
+                       return -ENOMEM;
                }
+               spin_lock_init(&portdata->lock);
 
                usb_set_serial_port_data(port, portdata);
 
 
        sierra_setup_urbs(serial);
 
-       return (0);
+       return 0;
 }
 
 static void sierra_shutdown(struct usb_serial *serial)
 
                for (j = 0; j < N_IN_URB; j++)
                        usb_unlink_urb(portdata->in_urbs[j]);
-               for (j = 0; j < N_OUT_URB; j++)
-                       usb_unlink_urb(portdata->out_urbs[j]);
        }
 
        /* Now free them */
                                portdata->in_urbs[j] = NULL;
                        }
                }
-               for (j = 0; j < N_OUT_URB; j++) {
-                       if (portdata->out_urbs[j]) {
-                               usb_free_urb(portdata->out_urbs[j]);
-                               portdata->out_urbs[j] = NULL;
-                       }
-               }
        }
 
        /* Now free per port private data */